Process of producing pig iron



Oct. 13, 1942.

C. R. HQLZWORTH PROCESS OF PRODUCING PIG IRON Filed July 25, 1940 2Sheets-Sheet 1 Fig. 5. Regular Pig Iron UHFHI'IHI'MIOO Diam.

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Fig. 6. Rl-gular Pig lrnn l'lulml -l00 Diam.

, 2. Graphilizml Pig Imn IIh'hml H1O Dian].

Oct. 13, 1942. c. R. HOLZWORTH 2,298,483

PROCESS OF PRODUCING PIG IRON Filed July 25, 1940 2 Sheets-Sheet 2 Fig.3. Graphilizml Pig Imn Fig. 7. lh'gular Pig lrun L'm'll'lu-d 500 [)iam.m-lvhml 500 Hiam.

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Patented Oct. 13, 1942 UNITED STATE s PATENT OFFICE raocass or rno ncmePIG IRON Charles B. Holzworth, North Tonawanda, N. Y.

Application July 25,- 1940, Serial No. 347,369 Claims. (ems-131) Thisinvention relates 'to methods for producing pig iron in the blastfurnace.

As is well known, the bulk of commercial pig iron is produced from thehematite and limonite iron ores. This is because these ore deposits arelarger, are more plentiful, and are more accessible, and also becausethis type of ore is easier and more economical to reduce or smelt in theblast furnace. Commercial pig iron produced from these ores usuallycontains from 3.0% to 4.25% in total carbon and in excess of 1.0% ofsilicon. The total carbon in the pig is composed of combined carbon andfree carbon. The combined-carbon content is usually between 35% and .80%and is for the most part in the form of cementite or iron carbide(FeaC). The free carbon content is in the form of separated collectionsof graphite distributed in the iron matrix, and which precipitates outof liquid solution while cooling to solidus and to atmospheretemperatures. As a rule, castings made from pig are rendered softer ormore machinable in proportion to the amount of free carbon present andalso in proportion to the degree of uniformity of distribution of thegraphite collections. Within certain limits, the silicon in the pig ironhas the effect of reducing the amount of combined car-' bon present, andconsequently, the chill in the casting made therefrom, and it also has agraphitizing eifect, but silicon also has the eilfect of reducing thetotal carbon and the solubility of carbon in pig iron. These effectsvary in proportion to the amount of silicon present. Hence, the lowerthe percentage of silicon present in the pig iron the finer and moreuniform is the grain, but with an increased hardness. v

Generally speaking, the major fault or disadvantage experienced withprior art pig iron, is that inthe castings made therefrom the'freecarbon or graphite is flake-like or vein-like in structure, and that thegraphite formations are not as uniformly distributed in the iron matrix,as is desired, and also that the graphite has the tendency to formoccasionally in relatively large concretions or lumps. Because of thistendency to have a relatively non-uniform distribution'of the graphiticcarbon, the castings made from. the conventional prior art pig iron areirregular in hardness and consequently are relatively low inmachinability. The relatively long flake-like or vein-like.graphiteformations of the typical prior art pig iron tend to formcleavage'planes in the matrix of the pig, and in the casting madetherefrom, which results in a relatively weak structure and one havingrelatively low tensile and trans-. verse strength. Also, because of thevein-like One of the principal objects of this invention is to provide anew and improved method for proa distinctly superior product; which pigiron or product has a uniform and relatively close or tight grain, andis also a heavy scrap carrier in the foundry, and which pig ironproduces sound castings with a minimum of shrinkage and chill, andcastings having increased tensile and transverse strength, and ofimproved machinability,

Further objects are to provide an improved method for producing adistinctly superior pig iron from the typical and plentiful hematite andlimonite iron 'ores and at little or no greater cost than conventionalpig iron of the prior art.

Still further objects will be apparent to those skilled in this art froman understanding of the following description and the accompanyingdrawings, in which drawings- Figures 1, 2, 3, and 4 are photomicrographsshowing enlargements of the grain structure of the same sample of pigiron, which sample was produced in accordancewith the present invention.Fig.1 shows the sample as unetched and at 100 magnifications; Fig. 2shows the. sample at 100 magnifications after being etched with a 2%nital solution; Fig. 3 shows the sample as unetched at 500magnifications; and Fig. 4 shows the sample at 1000 magnifications afterbeing etched with a 2% nital solution.

Figures 5, 6, 7, and 8 are photomicrograps showing enlargements of grainstructure of the same'sample of a conventional pig iron produced inaccordance with known standard methods of the prior art. Fig. 5 showsthe sample of conventional pig as unetched at 100 magnifications andshould be compared with Fig. 1 Fig. 6 shows the sample of conventionalpig at 100 magnifications after being etched with a 2% nital solutionand this figure should be compared with Fig.

2; Fig. 7 shows the sample of conventional pig iron as unetched at 500magnifications and this figure should be compared with Fig. 3; and Fig.8

shows the sample of conventional pig iron at 1000 magnifications afterbeing etched with a 2% nital solution, and this figure could be comparedwith Fig. 4.

In the drawings, the dark portions are the graphite particles, and thelight portions are the iron constituents, such as separately formedferrite and cemcntite, and" pearlite, which is the pearl-like striatedstructure and is a combination of ferrite and cementite. From anexamination of Figs. 5, 6, 7. and 8, it willbe noted that thegeneralcharacter of thegraphite shown therein is clearly flake-like orvein-like in its formation and also that there is a distinct tendencyfor the graphite to form in relatively large concretions or lumps which,as stated above, re-

sults in defects in castings made therefrom. However, the graphiteformation in Figs. 1, 2, 3, and 4 which is the pig iron of the presentinvention, is decidedly different from that appearing in Figs. 5, 6, '7,and 8. In Figs. 1, 2, 3, and 4 the raphite is clearly broken up intorelatively small particles; i. e., the graphite is in a finely dividedform, as distinguished from the relatively large concretions and thevein-like or flake-like formations of the ordinary or conventional pigiron appearing in Figs. 5, 6, 7, and 8. Furthermore, it will be apparentthat the finely divided graphite of Figs. 1, 2, 3, and 4 is evenlydispersed throughout the iron matrix, and the graphite of Figs. 5, 6, 7,and 8 is not so evenly dispersed. It is clearly apparent from acomparison of Fig. 4 with Fig. 8, that the pearlite laminations of theiron producedin accordance with the present invention is much finer thanthe pearlite laminations of ordinary iron produced in accordance withthe usual or conventional methods of the prior art. The analysis of theiron of Figs. 1, 2, 3, and 4 is as follows: silicon, 2.90%; totalcarbon, 4.07%; combined carbon .49%; titanium, .41%; Brinell, 179. Theanalysis of the iron of Figs. 5, 6, 7, and 8 is as follows: silicon,3.00%; total carbon, 3.86%; combined carbon, .41%; Brinell, 146.

The preponderance of finely divided graphite and the relatively evendispersion of the graphite in Figs. 1, 2, 3, and 4 are beneficialresults flowing from my improved method. One of the principal factorscausing these beneficial results is the absorption of titanium in ahighly reactive and effective form in the molten iron while-in the blastfurnace and the retention of titanium in a reactive and effective formin the solid pig iron.

The improvedmethod of this invention may be carried out in any wellknown form of blast furnace, and because of this it is thoughtunnecessary for an illustration of such a furnace to be included herein.It will be understood, however, that the conventional blast furnaceincludes the usual tall, cylindrical stack lined with refractoryfire-brick and provided with a charging opening or throat at its top andwith sepaabove explained, these ores are used because they are moreaccessible and are easier and more economical to reduce or smelt in theblast furnace. Such ores intheir natural state contain only a trace orsubstantially no titanium; that is, the titanium content is rarely over.1%.

In accordance with the present invention, a titanium-bearing material isalso added to the blast furnace burden. It is to be noted that in so faras the broader aspects of this invention are concerned,the-titanium-bearing material may be any material suitable for thepurpose. As an example, this material may be a titanium are such asrutile or ilmenite; or, it may be a waste product from the operation ofthe electric furnace engaged in reducing bauxite in the production ofaluminum. This waste product is in the form of a sludge and usuallycontains from 2% to 5% titanium (Ti), 50% iron (Fe), and 7% silicon(Si). A typical analysis for ilmenite is: 50% iron oxide (Fezoa); 45%titanium oxide (T102); 3% silica (SiOz); etc.

- To the burden thus far described, which is composed of a hematite ironore and a titanium-bearing material, there is added definite proportionsof fluxing material such as limestone, and also, if there is not enoughsilica present in the iron ore itself to produce a pig containing inexcess of 1% silicon, as stated previously, and'to prorate openings atdifierent levels at its bottom for tapping slag and molten iron,respectively. Approximately the lower eight feet of the furnace iscalled the hearth or crucible, and above that extends the wideningportion, called the bosh, which extends upward to that portion of thefurnace having the greatest diameter. The stack extends from the bosh tothe throat. As is well known, the blast furnace charge is'introducedinto the'throat or top of the stack in alternate layers of material;viz., ore, coke, limestone, etc., and the preheated air for combustionof the coke is introduced into thefurnace through the tuyeres at the topof the hearth. The combustion zon is at and above the tuyeres, and themolten slag layer is below the tuyeres and floats on the molten ironwhich collects in the furnace bottom.

In accordance with one aspect of the present invention, the improvedmethod includes the charging of the blast furnace with a burdencontaining as its main source of iron, a hematite or limonite iron ore.A typical example of such an ore is a Lake Superior hematite analyzingapproximately 73.50% iron cxide (F8203) 8% silica (SiOz), 2.5% alumina(A1203), and other normal constituents such as phosphorus and manganese,usually not exceeding a few tenths of 1%. As

duce the desired normal, or ordinary, content of silica in the slag,there is added an additional silica-bearing material, such as silicarock. This burden is charged into the blast furnace in the usual mannerand along with sumcient amounts of carbon in the form of coke. Air forsupporting combustion'of the coke is introduced at relatively hightemperatures through the tuyres to effect eflicient reduction orsmelting of the mate rials charged and to efiect the production ofmolten iron, containing titamium, silicon, etc.

In accordance with the present invention, the blast furnace is sooperated that the temperature reached in the reduction zone and in thecombustion zone is at least high enough to reduce the oxide of titanium,if the titanium .is present as an oxide in the charge, or to melt thetitanium if it is present in the charge as some other compound oftitanium. The theoretical reduction temperature of titanium oxide (TiOz)is on the order of 2962 F. and the theoretical temperature of fusion ofpure titanium (Ti) is on the order of 3280" F., and above. The exactform of the titanium in the molten iron thus produced cannot be statedwith absolute certainty. It may be in the form of elemental titanium(Ti) or in the form of some reactive and effective compound of titanium,for example, titanium carbide (TIC). I believe the titanium is producedin the form of titanium carbide (TiC), because incandescent carbon ispresent in the reducing atmosphere of the high temperature combustionzone. It seems unlikely that a nitride or some other reactive ,formwould be produced under these conditions.

desired quantity and character of slag, as explained hereinafter. It isessential for this purpose that the air blast temperature be in excessof 1500 F. to 1600 F., or even higher if practical slag volume I withthe equipment available.

After the molten iron containing titaniumis formed, as just'e'xplained,the next concern. is

. normal slag volume and keeping the basicity of to increase itstemperature to a point where the titanium in a reactive and effectiveform is completely dissolved in the molten iron.v This is done by aselecting and proportioning the materials of the charge that theslag-forming constituents thereof will be of such a quantity and quahtythat a larger-than-normal slag volume will be maintained in the furnace.The term larger-than-normal slag volume as used herein, is intended tomean that the volume of slag maintained in the furnace in-accordancewith the present invention is greater than that which is usuallymaintained at the present time in a blast furnace when operating toreduce iron ore in the conventional manner. At the present time, the rawmateirals are beneficiated and the slag volumes are usually below 1000pounds for each ton of iron. Therefore, the volume of slag maintained inaccordance with this invention should be sufficient to produce over 1000pounds for each ton of iron produced. Preferably, the.

should be between 1000 and 1500 pounds per ton of iron, and better stillbetween 1300 and 1500 pounds per ton of iron produced.

The l arger-than-n ormalslag volume performs the additional function ofa protecting cover for the .molten iron in the crucible. Furthermore,the

slag shouldbe basic in character. For the present purpose the combinedor total magnesium oxide and calcium oxide content (MgO-i-CaO) of theslag should exceed 42%, and preferably should be between 44% and 48%.The higher basicity of the slag raises the fusion temperature thereofandthereby results in a higher temperature for a given viscosity ofslag. The larger-than-nor'mal slag volume results in extending the timeof contact between the molten iron containing titanium and the slagOtherwise, the characteristics of the slag are similar to the generallyaccepted or standard blast furnace practice in the production of foundrygrades of pig iron; wherein the silicon content in the pig iron exceeds1%, as stated previously herein. As an example, "the silica content inthe slag is usually kept between'33% and 38% and the alumina between 11%and 16%. It is noted, however, that in the known and accepted methods ofproducing foundry grades of pig iron the silica content in the slag israrely, if ever, permitted to fall below 30% or to be in excess of and amaximum figure for alumina in the slag is considered to be 18%. P

As stated above, an important function per-, formed by the relativelyhigh air blast temperature, the larger-than-normal slag volume, and thebasic quality of the slag, superheated in passing through the slag'layer to a point where the titanium in its'previously explainedreactive and effective form, is completely absorbed in the molten iron.The theoretical temperature of absorption of reactive titahium andincluding its carbides intohomogeheous solution in iron is on the orderof 3100 F. The absorption will begin around 2800 and continue until itreaches and passes the 3100 F Heretofore, these temperatures havecombustion zone and thereby increase the emciency of reduction.

It is also important to note thatbecause of the larger-than-normal slagvolume, its high basicity, and the relativeiyhigh air blast temperature,the molten iron is superheated in passing through the slag layer so thatits temperature is raised to a point critical to the absorption ofcarbon in the molten iron in such a manner that, when the iron cools tothe solidus, the free or graphite carbon separated out'will be in finelydivided form and uniformly distributed throughout the iron matrix, likethat shown in Figs. 1, 2, 3, and 4 and as distinguished from theflakelike and lumpy graphite formations of Figs. 5, 6, '7, and 8. Thiscritical point is on the order of 3000 F.

The effect of superheating the molten iron is to cause the absorption ofa larger amount of car- 'bon in the molten iron, and, as stated above,the maximum temperature reached is such that the graphite carbon will bein finely divided form tion in that it acts apparently in the nature ofa catalyst and locks or fixes the carbon in the liquid metal, so thatwhen the iron passes through the solidification range the graphiticcarbon is retained in a finely divided and evenly dispersed form. Thetotal carbon present in the iron is therefore higher than normal and thegraphitic carbon is distributed uniformly and in finesubdivision'sthroughout the iron matrix.

A further and most beneficial characteristic is that the finelydividedcharacter of the graphitic carbon and its uniform distribution inthe pig iron carries through'lto and persists in the castings madetherefrom, and while the casting is slightly higher 'inBrinell hardnessbecause of its relatively fine pearlitic structure, it is a moremachinable casting having a fine, tight grain and one which hasincreased tensile and transverse is that the iron is been considered toohigh to be practical in the normal operation of a blast furnace; butthey have been obtained in accordance with the present invention bymaintaining the larger-thanstrength. Thus, the superior pig made fromthe present method is a heavy scrap carrier in the foundry and producessound castings with a minimum of chill and shrinkage; By the expressionheavy scrap carrier" is meant that the same quality of casting can beproduced with the pig iron of the present invention by using a higherratio of scrap to pig than can be done with the pig iron of the priorart.. The titanium present in the iron seems to assist the silicon tocarry out its beneficial effect of reducingchill, and it also seems toprevent the normal action of the v silicon from reducing the totalcarbon in the iron.

A grain structure is provided which is pearlitie in character, withfinely divided graphite uni formly distributed throughout, asdistinguished from the relatively lower carbon and .thesegregatedflake-like and lumpy graphite formations of "the prior artpig.

As an example of the manner in' which the contents of the charge shouldbe proportioned in order to obtain the larger-than-normal slag volume(over 1000 pounds per ton of iron produced) and the high basicity of theslag (in exv cess of 42 which as explained above are large- 1yresponsible for the complete absorption of the 'ilmenite, analyzing 50%FezOa, 45% T102, 3% S102 and traces of other elements, a typical ac--tual charge isas follows:

other constituents of the charge, those skilled in the art will readilyunderstand how a desired burden should be computed to produce ahighcarbon, titanium-bearing pig, such as given above. Experience showsthat the air blast temperature should exceed 1250 F. and should be ashigh as practical with the equipment available.

'The following is a table showing a number of actual results obtained atdifferent times by practicing the present invention, as explained above.These results show the bearing which the values of the slag volume andthe air blast temperature Pounds Hematite 9,860 Ilmem'te 140 Silica rockor other silica-bearing material- 200 Limestone 3,000 Coke 5,000

The above charge when smelted, produced 5,500 pounds of pig iron and3,465 pounds of slag.

The slag volume, when proportioned, amounts to 1,414 pounds of slag perton of iron. The pig iron produced amounted to 5,120 pounds of pure iron(Fe), as pig iron contains 93% Fe and 7% total silicon, carbon,manganese, phosphorus, ti-

tanium, etc. The titanium content in the pig amounted to .48%. Thebasicity of the slag approximated 46%, combined MgO and CaO and, thesilica approximated 34% and the alumina 14%. f I

A second example of a blast furnace charge computed in accordance withthe present invention and using thesame hematite ore but using theaforementioned by-product sludgeas the titanium-bearing material whichanalyzes 2-5% Ti, about 50% Fe, and 7% Si, is as follows:

' Pounds Hematite -e 8,400 Sludge 1,600 Silica ro 112 Limestone 3,000Coke 5,000

invention, it has been determined that upon smelting a charge like theexamples given above, approximately 75% of the titanium present in thecharge passes into the pig iron, the remaining being in. the slag. Theamount of titanium in the pig iron is, of course, a function of theamount of titanium in the charge and that percentage of titanium in thecharge which is absorbed in'the iron matrix. Experience shows that thepercentage of titanium present in the charge which is absorbed in theiron, varies with the value of the slag volume maintained in thefurnace, the basicity of the slag, and the air blast temperature; i. e.,as the slag volume, slag basicity and air blast temperature increase theamount'of titanium in the-pig increases. As the amount of slag is afunction of the amount of slag-forming constituents of the charge (suchas gangue in the ore, silica-rock, limestone, etc.);

and, as the basicity of the slag is determined by the quantity oflimestone in proportion to the have on the amount of the carbon andtitanium constituents in the pig iron, and also show the influence ofthe titanium present on the amount' of total carbon present in the pigiron. The silicon in the pig is also included so as to indicate itsinfluence when comparing the several results.

Analysis oi pig Slag Air blast Cast No.- volume oi temperpig nture SiTztal Tl per ton F. Percent Percent Percml l, 030 1, 300 3. 02 3. 30 1,030 l, 300 3. 03 3. 35 l, 200 1, 300 3. 00 3. 35 1, 200 1, 500 3. 00 4.00 35 l, 200 1, 600 8. 28 3. 79 30 1, 400 l, 500 3.10 3. 95 45 l, 400 l,550 3. 08 3. 98 45 1, 500 1, 600 3. 11 3. 96 48 l, 500 1, 600 2. 83 4.1042 1, 500 l, 600 2. 26 4. l8 35 It has been found that pig iron producedin accordance with the above described process and containing in excessof .25% Ti, possesses distinctly superior qualities; and, when made intocastings, produces good and sound castings, having a line, tight grain,a minimum of shrinkage and chill, increased tensile and transversestrength, and improved machinability. An examination of the pig shows adistinct preponderance of finely divided graphite and pearlite,uniformly distributed throughout. These superior qualities of the pigare carried through into the casting and thereby render this pig iron aheavy scrap carrier in the foundry. All other factors remaining thesame, the above-explained superior qualities are present to a degreeproportional to the amount of Ti present in the pig. An upper practicallimit for the titanium content of the pig iron is believed to be on theorder of 1.0%. A practical optimum range for the titanium content isbetween 30% and .50%, with the most desirable range between .40% and.50%. It will be appreciated that the desired titanium content of thepig will depend upon the amount of scrap to be used with the pig in thecupola. The higher the percentage of scrap, the higher the titaniumcontent iii th pig should be. It has been found in practicing thepresent invention, that castings made from 100% direct metal from theblast furnace, and without any scrap, produce a 50% increase in tensilestrength as the following will -A further actual comparable result in afoundry, and illustrating the superior qualities of the pig ironproduced in accordance with the present invention over the prior artpig, is as These results show an increase in combined carbon in thecasting when pig iron produced in accordance with the present inventionis used, and they show a higher Brinell due to the pearlitic grainstructure. These results also show that the machinability of the castingis improved even though the Brinell is higher, and that the tensile andtransverse strength is materially increased.

As the above results show that the outlined desirable characteristicspresent in the pig iron are carried through to castings made therefrom,7 it is evident that when titanium is produced in v a blast furnace andadded to the molten iron by the improved method and process describedabove, such titanium is retained in the solid pig iron in a highlyreactive and effective form. The

identity of its precise form and an explanation of exactly how it isretained in the solid are not critical to a thorough understanding of myimproved method by those skilled in this art. I believe that thetitanium which is produced and added to the molten iron in the blastfurnace in the manner previously explained, is titanium carbide (TiC)and that it is retained in solid solution in the solid pig iron. Threason for my conclusion is that titanium and its several probablecompounds, are very hard and consequently, if the titanium weresuspended in the solid iron as a separate phase, hard spots would bepresent, which is not true of iron produced by my method.

What I claim and desire to secure by Letters Patent of the United Statesis:

1. The method of producing in a blast furnace a foundry grade pig ironof improved, refined and controlled graphitic structure containing inexcess of 25% Ti in a reactive and effective form and in excess of 1%Si, which method comprises charging th furnace with an iron orecontaining in its natural state substantially no titanium,

and constituting the principal source of iron, to-

gether with limestone, a titanium-bearing mate- 2. The method ofproducing in a blast furnace a foundry grade pig iron of improved,refined and controlled graphitic structure containing in excess of .25%Ti in a reactive and effective form and in excess of 1% Si, which methodcomprises charging the furnace with an iron ore containing in itsnatural state substantially no titanium, together with limestone, atitanium-bearing material in sufilcient quantity to produce theaforementioned titanium content in the pig iron, said iron ore and saidtitanium-bearing material constituting the principal source of iron, andwith sufiicient coke to reduce the oxides present in the charge;regulating the proportions of the constituents of the charge to maintaina slag volume in the furnace suflicient to produce from 1300 to 1500pounds of slag for each ton of iron produced, and to produce a basicslag containing in excess of 42% combined CaO and MgO; and

smelting such charge using air temperatures in excess of 1250 F.

3. The method of producing in a blast furnace a foundry grade pig ironof improved, refined and controlled graphitic structure containing inexcess of 25% Ti in a reactive and effective form and in excess of 1%Si, which method comprises charging the furnace with an iron orecontaining in its natural state substantially no titanium, together withlimestone, a titanium-bearing material in sufiicient quantity to producethe aforementioned titanium content in the pig iron, said iron ore andsaid titanium-bearing material constituting the principal source ofiron, and with sufiicient coke to reduce the oxides present in thecharge; regulating the proportions of the constituents of the charge tomaintain a slag volume in the furnace sufficient to produce from 1000 to1500 pounds of slag for each tone of iron produced, and to produce abasic slag containing 4. The method of producing in a blast furnace afoundry grade pig iron of improved, refined and controlled graphiticstructure containing in excess of .25% Ti in a reactive and effectiveform and in excess of 1% Si, which method comprises charging the furnacewith an iron ore containing in its natural state substantially notitanium, together with limestone, a titanium-bearing material insufilcient quantity to produce the aforementioned titanium content inthe pig iron, said iron ore and said titanium-bearing materialconstituting the principal source of iron, and with suflicient coke toreduce the oxides present in the charge; regulating the proportions ofthe constituents of the charge to maintain a slag volume in the furnacesufiicient to produce from 1300 to 1500 pounds of slag for each ton ofiron produced, and to produce a basic slag containing between 44% and48% combined CaOand MgO; and smelting such charge using air temperaturesin excess of 1250 F.

5. The method of producing in a blast furnace a foundry grade pig ironof improved, refined a o 1 controlled graphitic structure containing inexcess of 25% Ti in a reactive and effective form and in excess of 1%Si, which method comprises charging the furnace with an iron orecontaining in its natural state substantially no titanium, together withlimestone, a titanium-bearing material in sufficient quantity to producethe aforementioned titanium content in the pig iron, said iron ore andsaid titanium-bearing material constituting the principal source ofiron, and withv duced, and to produce a basic slag containing in excessof 42% combined C20 and MgO; and

suflicient coke to reducethe oxides present in, the charge; regulatingthe proportions of the constitsmelting such charge using airtemperatures in uents of the charge to maintain a slag volume excess of1250 F.

in the furnace sufficient to produce from 1000 to 5 1500 pounds of slagfor each tone of iron. pro- CHARLES R. HOLZWORTH.

